Field of the Invention
The aspect of the embodiments relates to an image sensor and an imaging apparatus.
Description of the Related Art
In recent years, imaging apparatuses such as digital cameras and smart phones have become popular. These imaging apparatuses are provided with an automatic focus (AF) function of being automatically focused on a subject (adjusting a lens focus position), allowing a user to capture an image of the subject without performing focus adjustment.
Some models of such digital cameras and smart phones employ an imaging plane phase difference AF method in which a phase difference AF method is performed based on output data of pupil-divided phase difference pixels provided on the imaging plane of an image sensor for capturing a subject.
The phase difference AF method refers to an AF method based on the idea that, when a subject is in focus, the positions of two images with different image forming positions are fixed. More specifically, since the distance between the two images is fixed when the subject is in focus, the phase difference AF method calculates the defocus amount indicating how much the lens focus position is deviated from the current lens position based on phase difference information indicating the distance between the two images. Then, the method moves the focus lens to the lens focus position based on the calculated defocus amount, thus achieving focusing.
The above-described phase difference AF method enables obtaining the defocus amount from image data of one frame, remarkably reducing the time required to be focused on the subject and hence achieving high-speed focusing. Japanese Patent Application Laid-Open No. 2016-9043 discusses an image sensor mounting a function of performing correlation calculation based on an imaging plane phase difference AF method.
However, if the number of phase difference pixels used for the imaging plane phase difference AF method is increased intending to improve the AF calculation accuracy and reliability, the time required to calculate the defocus amount will be prolonged.